The fabrication of microelectronic components from a microelectronic workpiece, such as a semiconductor wafer substrate, polymer substrate, etc., involves a substantial number of processes. For purposes of the present application, a microelectronic workpiece is defined to include a workpiece formed from a substrate upon which microelectronic circuits or components, data storage elements or layers, and/or micro-mechanical elements are formed.
There are a number of different processing operations performed on the workpiece to fabricate the microelectronic component(s). Such operations include, for example, material deposition, patterning, doping, chemical mechanical polishing, electropolishing, and heat treatment. Material deposition processing involves depositing thin layers of material to the surface of the workpiece. Patterning provides removal of selected portions of these added layers. Doping of the microelectronic workpiece is the process of adding impurities known as “dopants” to the selected portions of the microelectronic workpiece to alter the electrical characteristics of the substrate material. Heat treatment of the microelectronic workpiece involves heating and/or cooling the microelectronic workpiece to achieve specific process results. Chemical mechanical polishing involves the removal of material through a combined chemical/mechanical process while electropolishing involves the removal of material from a workpiece surface using electrochemical reactions.
Numerous processing devices, known as processing “tools”, have been developed to implement the foregoing processing operations. These tools take on different configurations depending on the type of workpiece used in the fabrication process and the process or processes executed by the tool. One tool configuration, known as the Equinox(R) wet processing tool and available from Semitool, Inc., of Kalispell, Mont., includes one or more workpiece processing stations that utilize a workpiece holder and a process bowl or container for implementing wet processing operations. Such wet processing operations include electroplating, etching, cleaning, electroless deposition, electropolishing, etc.
In accordance with one configuration of the foregoing Equinox(R) tool, the workpiece holder and the processing container are disposed proximate one another and function to bring the microelectronic workpiece held by the workpiece holder into contact with a processing fluid disposed in the processing container thereby forming a processing chamber. Restricting the processing fluid to the appropriate portions of the workpiece, however, is often problematic. Additionally, ensuring proper mass transfer conditions between the processing fluid and the surface of the workpiece can be difficult. Absent such mass transfer control, the processing of the workpiece surface can often be non-uniform.
Conventional workpiece processors have utilized various techniques to bring the processing fluid into contact with the surface of the workpiece in a controlled manner. For example, the processing fluid may be brought into contact with the surface of the workpiece using a controlled spray. In other types of processes, such as in partial or full immersion processing, the processing fluid resides in a bath and at least one surface of the workpiece is brought into contact with or below the surface of the processing fluid. Electroplating, electroless plating, etching, cleaning, anodization, etc. are examples of such partial or full immersion processing.
Existing processing containers often provide a continuous flow of processing solution to the processing chamber through one or more inlets disposed at the bottom portion of the chamber. Even distribution of the processing solution over the workpiece surface to control the thickness and uniformity of the diffusion layer conditions is facilitated, for example, by a diffuser or the like that is disposed between the one or more inlets and the workpiece surface. A general illustration of such a system is shown in FIG. 1A. The diffuser 1 includes a plurality of apertures 2 that are provided to disburse the stream of fluid provided from the processing fluid inlet 3 as evenly as possible across the surface of the workpiece 4.
Although substantial improvements in diffusion layer control result from the use of a diffuser, such control is limited. With reference to FIG. 1A, localized areas 5 of increased flow velocity normal to the surface of the microelectronic workpiece are often still present notwithstanding the diffuser 1. These localized areas generally correspond to the apertures 2 of the diffuser 1. This effect is increased as the diffuser 1 is placed closer to the microelectronic workpiece 4 since the distance over which the fluid is allowed to disburse as it travels from the diffuser to the workpiece is decreased. This reduced diffusion length results in a more concentrated stream of processing fluid at the localized areas 5.
The present inventors have found that these localized areas of increased flow velocity at the surface of the workpiece affect the diffusion layer conditions and can result in non-uniform processing of the surface of the workpiece. The diffusion layer tends to be thinner at the localized areas 5 when compared to other areas of the workpiece surface. The surface reactions occur at a higher rate in the localized areas in which the diffusion layer thickness is reduced thereby resulting in radially, non-uniform processing of the workpiece. Diffuser hole pattern configurations also affect the distribution of the electric field in electrochemical processes, such as electroplating, which can similarly result in non-uniform processing of the workpiece surface (e.g., non-uniform deposition of the electroplated material).
Another problem often encountered in immersion processing of the workpiece is disruption of the diffusion layer due to the entrapment of bubbles at the surface of the workpiece. Bubbles can be created in the plumbing and pumping system of the processing equipment and enter the processing chamber where they migrate to sites on the surface of the workpiece under process. Processing is inhibited at those sites due, for example, to the disruption of the diffusion layer.
As microelectronic circuit and device manufacturers decrease the size of the components and circuits that they manufacture, the need for tighter control over the diffusion layer conditions between the processing solution and the workpiece surface becomes more critical. To this end, the present inventors have developed an improved processing chamber that addresses the diffusion layer non-uniformities and disturbances that exist in the workpiece processing tools currently employed in the microelectronic fabrication industry. Although the improved processing chamber set forth below is discussed in connection with a specific embodiment that is adapted for electroplating, it will be recognized that the improved chamber may be used in any workpiece processing tool in which process uniformity across the surface of a workpiece is desired.